Fixed charge in the cell membrane.

1. Focal electric field was generated by passing a current of 5 x 10(-7) to 1 x 10(-5) A from a micropipette into the culture medium. Movement of cells at a distance of 5-50 mu from the electrode tip was observed. In case of cells embedded in the culture only local deformation of the membrane was observed.2. The cell species explored included neurones, glia, muscle fibres, connective cells, malignant cells and erythrocytes. All cells responded in a similar manner to the electric field, and the current required was in the same range.3. Cells were attracted to a positive micropipette and repelled from a negative one: the only exception was observed in certain malignant cells which moved in the opposite direction.4. Movement and membrane deformation could be obtained with electrodes filled with various concentrated and isotonic solutions. The composition of the culture medium also had no qualitative influence on these effects.5. Metabolic poisons or rupture of the cell membrane had no effect on the movement. Isolated membrane fragments showed movement similar to that of intact cells.6. The possibility of artifacts due to proximity of the focal electrode is considered. It is shown that electro-osmosis cannot account for the present observations. Some other artifacts are also excluded.7. It is proposed that the most satisfactory way to account for the present observations is by a membrane carrying negative fixed charge of the order of 2.5 x 10(3) e.s.u./cm(2). Some physiological consequences of presence of negative charge in the membrane are briefly discussed.